Steps to write with "invisible ink" mixture -- help your VBS Teacher 2016

from KIDZ World dot-com:

Mix about 1/4 cup (60 ml) of baking soda and 1/4 cup (60 ml) of water. Next, write using a Q-tip, toothpick or brush on a piece of paper. Let it dry completely. To read the secret message, paint grape juice concentrate across the paper with a paint brush or a sponge. Don't forget - grape juice stains.
Why it works: Grape juice has an acid that reacts with the baking soda. A different color appears wherever the secret message is written.

http://www.kidzworld.com/article/3844-making-invisible-ink-appear